1987 mariner magnum 150

[MG860310]

My outboard is overheating after replacing the water pump and thermostat and temperature sensor. I’m not a boat mechanic so I’ve had friends helping me that have some knowledge. Any help would be appreciated

 

[jimmbo]

Under what condition is it overheating? Idle? Full Throttle? All speeds? Where has the engine been run the most of its life. lakes, river, ocean? What condition was the old Impeller?

 

[MG860310]

It doesn’t overheat at idle only at higher rpm. I put muffs on it and ran in gear and out of gear and after about 10 minutes it will climb in temperature and start to beep. The old impeller was in good condition the old thermostat was in good condition
The boat has never been in salt water just inland lakes in Ohio and Pennsylvania. I also replaced the plugs and it fires up with no issues and spits water consistently.

 

[jimmbo]

Running the engine on muffs, is no indication the water pump is actually doing anything.
That engine has 2 stats, and a Pressure Valve, that allows more cooling water at higher engine speeds. Did you verify that the stats actually open? and that the pressure valve isn't stuck shut?

 

[MG860310]

I didn’t know that it had 2 stats I did check the one and it opens. I’ll check the other tomorrow and I have know idea where the pressure valve is located

 

[MG860310]

I didn’t know that it had 2 stats I did check the one and it opens. I’ll check the other tomorrow and I have know idea where the pressure valve is located

 

[MG860310]

so both stats open and work with no problems. I ordered a new poppet valve kit and when I went to replace it I noticed the cover is broke and after looking online for it I see 2 different styles. I've added pictures because I'm confused why in the cooling diagram it shows a hose going from the top to the poppet and then I see another diagram on the parts list that it is plugged and no water hose.

 

[Faztbullet]

That cover is cut like that from factory ..its not broke. Also that water diagram is not correct for your year/liter motor

 

[MG860310]

Ok got it. Now why would I still be overheating if the water pump is good and the stats are good and the poppet works???